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The (Ground) Plane Truth

 
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kearney



Joined: 20 Sep 2008
Posts: 544

PostPosted: Thu May 03, 2018 4:47 pm    Post subject: The (Ground) Plane Truth Reply with quote

Hi

I'll be the first to admit that my knowledge of radio physics is exceptionally limited. This brings me to the question of ground planes. I am told that a ground plane does not require metal to metal contact with an antenna. Is this correct? The reason I ask is I am wondering if I should un-install antennas prior to paint?

Cheers

Les


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carl.froehlich(at)verizon
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PostPosted: Thu May 03, 2018 5:28 pm    Post subject: The (Ground) Plane Truth Reply with quote

Shoot fire, you might as well throw gas on the primer war fire....

Here is the deal. RF ground is a different animal from DC ground. I recommend you remove all external antennas prior to paint. After paint re-install the antennas using a star washer on the inside of the fuselage on the antenna mounting studs. Done.

I have years of running HF and VHF mobile antennas pumping out 100+watts that where on mag mounts. The mag mount itself had Mylar file between the magnet and the car - along with the car paint. This resulted in no metal to metal contact - Infinity DC resistance. The antennas were perfectly happy to be RF coupled to the car ground plane, just like RF is happy to pass through a capacitor. Add the star washer anyway just to have a locking device and a DC connection for noise (very low probability, but star washers are cheap).

But - no matter what you do check all antennas with a real antenna analyzer from the radio (so that you check your coax and all connectors). This is how you know stuff works before you fly. People call me up on radio problems and this is the first thing I do. I find broken antenna mounts, cut or pulled out coax and crimp connectors that are just ugly.

Have fun,
Carl
Quote:
On May 3, 2018, at 5:47 PM, kearney <kearney(at)shaw.ca> wrote:



Hi

I'll be the first to admit that my knowledge of radio physics is exceptionally limited. This brings me to the question of ground planes. I am told that a ground plane does not require metal to metal contact with an antenna. Is this correct? The reason I ask is I am wondering if I should un-install antennas prior to paint?

Cheers

Les




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http://forums.matronics.com/viewtopic.php?p=479827#479827











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kearney



Joined: 20 Sep 2008
Posts: 544

PostPosted: Thu May 03, 2018 5:51 pm    Post subject: Re: The (Ground) Plane Truth Reply with quote

Thanks Carl.

I assume most avionics shops would have an analyzer. Is this correct?

Cheers

Les


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Lenny Iszak



Joined: 23 Mar 2008
Posts: 246

PostPosted: Thu May 03, 2018 6:06 pm    Post subject: The (Ground) Plane Truth Reply with quote

Les,

The ground plane does requires electrical contact with the base of the antenna.

Lenny

Quote:
On May 3, 2018, at 8:47 PM, kearney <kearney(at)shaw.ca> wrote:



Hi

I'll be the first to admit that my knowledge of radio physics is exceptionally limited. This brings me to the question of ground planes. I am told that a ground plane does not require metal to metal contact with an antenna. Is this correct? The reason I ask is I am wondering if I should un-install antennas prior to paint?

Cheers

Les




Read this topic online here:

http://forums.matronics.com/viewtopic.php?p=479827#479827











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Lenny Iszak
Palm City, FL
2014 RV-10, N311LZ - 400 hrs
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carl.froehlich(at)verizon
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PostPosted: Thu May 03, 2018 6:12 pm    Post subject: The (Ground) Plane Truth Reply with quote

Just find your local ham radio operator that has something like this: https://www.gigaparts.com/mfj-259c.html?gclid=EAIaIQobChMI6Niipvzq2gIVV4ezCh3UVAUBEAQYASABEgL2VPD_BwE
Better yep, get one for you local EAA chapter as a shared tool.
Carl

On May 3, 2018, at 6:51 PM, kearney <kearney(at)shaw.ca (kearney(at)shaw.ca)> wrote:
Quote:
--> RV10-List message posted by: "kearney" <kearney(at)shaw.ca (kearney(at)shaw.ca)>

Thanks Carl.

I assume most avionics shops would have an analyzer. Is this correct?

Cheers

Les


Read this topic online here:

http://forums.matronics.com/viewtopic.php?p=479831#479831
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Kelly McMullen



Joined: 16 Apr 2008
Posts: 1115
Location: Sun Lakes AZ

PostPosted: Thu May 03, 2018 7:01 pm    Post subject: The (Ground) Plane Truth Reply with quote

Waste of time Les. If you properly installed the antenna with gasket and/or sealant

the paint shop should properly mask the antenna, so it doesn't get painted.

The grounding will be unchanged. On most com antennas, the ground path is through

the 3 or 4 screws that attach the antenna to the doubler you put under the fuselage skin.

The clean way to do that is to install nut plates on the doubler, then rivet doubler to inside of fuselage skin.

That way the ground is with the nutplates and solid via rivets to fuselage.

Good installs include a bead of sealant around the outside edge of the antenna.

Good paint shops protect antennas throughout skin prep and painting.

That said, be certain they protect the wheel bearings from pressure washing, or repack the bearings before the

plane rolls out of the shop.

Kelly

Quote:
Sent from my IBM-360 main frame


On Thu, May 3, 2018 at 5:47 PM, kearney <kearney(at)shaw.ca (kearney(at)shaw.ca)> wrote:
Quote:
--> RV10-List message posted by: "kearney" <kearney(at)shaw.ca (kearney(at)shaw.ca)>

Hi

I'll be the first to admit that my knowledge of radio physics is exceptionally limited. This brings me to the question of ground planes. I am told that a ground plane does not require metal to metal contact with an antenna. Is this correct? The reason I ask is I am wondering if I should un-install antennas prior to paint?

Cheers

Les




Read this topic online here:

http://forums.matronics.com/viewtopic.php?p=479827#479827






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Bob Turner



Joined: 03 Jan 2009
Posts: 824
Location: Castro Valley, CA

PostPosted: Thu May 03, 2018 10:04 pm    Post subject: Re: The (Ground) Plane Truth Reply with quote

I usually agree with Carl, but not this time. Capacitive coupling at RF frequencies usually has low impedance but does introduce an undesirable phase shift. Mag mount car antennas can be designed to balance this shift out, and some feed techniques (a gamma match as used in the Archer design) use a capacitor to introduce a desired phase shift. But standard aircraft antennas need a zero phase shift connection to ground. A good connection between the coax braid and the ground plane will suffice for simple antennas (nothing but a wire in the base). If the base has a matching network, then it will also need a good connection to the braid.

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jesse(at)saintaviation.co
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PostPosted: Fri May 04, 2018 4:14 am    Post subject: The (Ground) Plane Truth Reply with quote

I think the operative word is “should”. I have a plane in my hangar that is very nicely painted. However, the Paint shop painted over the data plate. It’s almost impossible to read it. Then they put their “painted by” sticker right next to the painted over data plate. What should happen is not always what does happen.

Jesse Saint
Saint Aviation, Inc.
352-427-0285
jesse(at)saintaviation.com

Sent from my iPad

[quote] On May 3, 2018, at 10:58 PM, Kelly McMullen <apilot2(at)gmail.com> wrote:

Waste of time Les. If you properly installed the antenna with gasket and/or sealant
the paint shop should properly mask the antenna, so it doesn't get painted


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